Silicon-on-insulator (SOI) substrates introduce harmonics into radio-frequency (RF) switches. Particularly, when an RF switch is formed on an SOI wafer, there can be undesirable device characteristics as a result of induced harmonics. An SOI wafer (also called an SOI substrate) includes an insulator layer on a silicon (Si) substrate and a semiconductor material layer on the insulator layer. In an RF circuit, the silicon layer provides that active components that can be wired together using any standard IC technology. The insulator layer may be a buried oxide (BOX) layer. The BOX layer is on top of a handle Silicon wafer, e.g., substrate, that typically is of higher resistivity in nature to reduce RF coupling. The interface between the BOX layer and the handle wafer (e.g., substrate) constitutes an inversion layer due to a fixed positive charge in the oxide and an induced negative mobile charge in the substrate. This mobile charge can react to the voltage signals produced by the active devices or wires themselves. This voltage response behavior of the handle wafer can be characterized as a variable capacitor (or varactor). An RF device such as a field effect transistor (FET) or wire formed in the silicon on the BOX carrying an RF signal will modulate the handle wafer varactor behavior, leading to non-linearities in the signal. This non-linear coupling causes unwanted distortions in the signal.
Selectively damaging regions in the Si substrate interrupts the inversion layer, which can interrupt the substrate coupling. For example, a trench may be formed in the BOX and an inert ion may be implanted at a high dose into the Si substrate through the trench. As an illustrative example, argon (Ar) may be implanted at an energy of 30 keV and a dose of 5e15/cm3. This disrupts the interface between the BOX and the substrate and reduces substrate coupling. However, this technique is not effective for isolating a FET island, such as that used with an RF switch, because the inert implant does not diffuse laterally under the FET. As such, the trench and implant technique is not useful for active devices such as an RF switch.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.